The invention relates to a disc brake with an electromechanical actuator, which is designed as an electric motor, for actuating an application device for applying the brake, which application device has a self-energizing device.
Disc brakes of this type are known per se. It has not hitherto been possible for them to become established in practice since no structurally and economically convincing concepts have been proposed, only concept studies.
Suitable as a self-energizing device is for example a ramp or wedge surface, against which is supported the brake lining which is moved not only perpendicularly to the brake disc but rather also in the rotational direction or parallel to the brake disc.
The application device can for example comprise a planetary gear set which is driven by an electric motor as an actuator. During an operation of the service brake, the planetary gear set actuates an element (for example an eccentric shaft) which deflects the actuating force and which, by means of a pressure plate, moves the brake lining in the circumferential direction of the brake disc so as to utilize the self-energizing effect. During an operation of the parking brake, the planetary gear set drives two self-locking threaded spindles, which are arranged in parallel, by means of an external gearwheel. The threaded spindles convert the introduced rotational movement into a linear movement of the spindle nuts, and thereby press the brake lining against the brake disc.
The planetary gear set of the arrangement is subjected to very high torques during braking processes. As a result of this loading and the relatively small available installation space in the wheel brake, it is necessary to use a relatively high-grade planetary gear set or other gearwheel mechanism.
Against this background, it is the object of the invention to specify an alternative concept for realizing a self-energizing disc brake which can be realized in a cost-effective manner. Also desirable is good efficiency, since this directly influences the required drive power of the electric motor.
The invention creates a disc brake with an electromechanical actuator, which is designed as an electric motor, for actuating an application device for applying the brake, which application device has a self-energizing device, with the electric motor acting directly, or via a gearing, on a rotary lever which acts on at least one brake piston which moves a brake lining parallel to the brake disc rotational axis, which brake lining is movable both in the direction parallel to the brake disc rotational axis and also parallel to the brake disc friction surface.
This concept can be implemented in a cost-effective manner in particular without expensive, high-precision parts, and offers the possibility of realizing good efficiency.
The invention makes it possible to realize a particularly reliable and simple-design self-energizing disc brake with electromechanical actuation, in the realization of which it is advantageously also possible to utilize known components from the field of pneumatic disc brakes for utility vehicles, such as rotary levers and their bearing arrangements, with an application parallel to the brake disc rotational axis being utilized to apply the brake linings even though these must also perform a movement in the circumferential direction during the braking process.
One particular advantage of the application perpendicular to the brake disc is also to be considered that the controller of the brake need not identify the movement direction of the vehicle when the brake is applied.
The electric motor, in a compact design, preferably has a linear gearing which acts on the rotary lever. Said linear gearing can be designed as a recirculating ball drive.
In order to ensure the mobility of the brake lining parallel to the brake disc friction surface, it is expedient if a bearing is arranged between the brake lining and the brake piston, which bearing realizes or permits the movement of the brake lining perpendicular to the application movement of the rotary lever, that is to say parallel to the brake disc friction surface.
It is also expedient if the brake piston is arranged parallel to at least one or more energizing pistons which, with their one end, are supported directly or via a bearing on the brake caliper and, at their other end, have, at least as a self-energizing device, at least one ramp surface which is inclined with respect to the brake disc friction surface. Here, an arrangement of the brake piston between two of the energizing pistons is particularly space-saving.
The energizing pistons preferably have double-acting ramp surfaces such that said energizing pistons act as ramp surfaces for self-energizing during braking during forward and reverse travel.
Here, it is expedient to arrange rolling bodies between the energizing pistons and the brake lining. The ramps are preferably formed in the energizing pistons and a recess is correspondingly formed in the lining, which recess engages around the rolling bodies in a substantially form-fitting fashion in the manner of a spherical cap and into which recess is inserted a bearing such as a plain bearing, such that the rolling bodies can roll on the ramps. Also conceivable, but less preferable, are an inverse arrangement with the ramps in the lining carrier plate and with a virtually form-fitting, for example spherical-cap-like recess in the energizing pistons or in an additional pressure plate, or else an embodiment with ramps in both elements.
It is expedient to arrange rolling bodies between the ramp surfaces of the energizing pistons and the brake lining.
The electric motor is also preferably connected to a control device for controlling the braking process, in order to control the self-energizing action as a function of the parameters present during the braking process. Here, it is possible to incorporate sensors and/or mathematical methods into the control.
FIG. 1 shows an embodiment, explained in more detail further below, with a constant ramp angle α between the ramps and the brake disc friction surface. Constant ramp angles, in particular degressively running ramp angles, are possible.
In this way, a particularly simple structural design is obtained which is characterized by a robust design, good functional reliability and low production costs. Here, balls are cost-effective rolling bodies which are virtually self-aligning in the ramp surface. To increase the load capacity, the balls can also run in matched running grooves.
A variant with rollers as rolling bodies would, in contrast, have a particularly small amount of hysteresis (not illustrated here).
Also contemplated is a variant in which the ramp angle of the recesses in the circumferential direction about the longitudinal axis of the adjusting nuts or brake pistons is not constant but rather variable, such that a ramp angle α of different gradient is present depending on the rotational position of the nuts. For this purpose, ball running grooves with different gradient are arranged for the different rotational positions.
It is thereby possible for the application characteristic to be varied in a simple manner by virtue of the nuts being rotated, for example by means of a separate adjusting actuator, preferably of electromechanical design (for example a further, relatively small electric motor), which rotates the nuts for example by means of a drive output shaft with a gearwheel, by virtue of said adjusting actuator, with the drive output wheel, driving one of the nuts for example at an external toothing of its flange, and the other nut being co-driven by means of a belt drive which is wrapped around the two nuts.
In this way, it is also possible to increase the degree of self-energizing which can be obtained in the limit region of the friction value. The switching can however take place only in the released state since the nuts cannot rotate during the applications of the brake.
The ramps can also describe an arc, such that the lining follows the geometry of the brake ring, or the ring geometry of the brake disc, during its movement.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.